Iron oxide is a general term that encompasses several different compounds:

* Iron(II) oxide (FeO): This is a pure substance with a specific chemical formula and composition.

* Iron(III) oxide (Fe₂O₃): This is also a pure substance with a specific chemical formula and composition.

* Iron(II,III) oxide (Fe₃O₄): This is a pure substance with a specific chemical formula and composition.

* Other mixed oxides: There are other less common iron oxides with varying proportions of iron and oxygen.

Therefore, if you are referring to a specific iron oxide with a defined chemical formula, then yes, it is a pure substance.

However, if you are referring to "iron oxide" in a general sense, then it could be a mixture of different iron oxides, and therefore not a pure substance.

For example, rust is a form of iron oxide, but it's not a single pure compound. It's a mixture of various iron oxides and other compounds.